Are you allowed to routinely erase CVR recordings at your airline solely at your discretion? I hope not...
Of course, that is what the button is there for.
Generally if you are on stand with the brake set and in a position to push the button the recording is not required, you are safely parked rather than being in a smoking hole.
If you have had a reportable incident or accident, and have survived, then you would be required to preserve the data for the investigation but otherwise we are quite free to erase the recording if we wish to.
The discussion in moot anyway, if the powers that be decide it is finally time to fit them, and Air India may just be the one that swings it, they will be fitted regardless of what we think.